In the prior art, the connection and accurate positioning of these two members is provided by means of spindles, one of the ends of which extends into an appropriate housing of the core plate by being axially slit in order to impart to it a relative resiliency in the transverse direction, the other end extending with a clearance through a bore of the flange of a cluster guide and being secured against movement with respect to the latter by screwing a nut coming in abutment against an inner shoulder of the bore so as to exert a reaction during the screwing on a threaded portion of the spindle. The nut is thereafter blocked on the flange, e.g., by soldering. By distributing over the flange periphery an appropriate number of such spindles and by providing for their coordinated tightening via the nuts associated thereto, accurate positioning of the flange with respect to the plate is achieved, notably so as to bring into alignment the vertical axes of these two members and to adjust to an accurately determined value the horizontal clearance between them.
The axially slit end is formed of two flexible branches the outer diameter of which is slightly greater than the receiving bore, formed in the upper plate of the core, assuring sure that after mounting there is no remaining clearance subject to vibrations and wear, and providing an adaptation to the position tolerances of the two spindle axes respectively on the core upper plate and on the cluster guide lower flange.
The two spindles are generally disposed in such manner that the slits are positioned perpendicularly with respect to one another.
This state affords the best compromise between strength and flexibility. However, the centering of the two parallel members takes place against the resisting section of the spindles, which must provide not only for the orientation and coincidence of the cluster guides with respect to the network of fuel elements underneath the core plate, but also for the holding of the lower ends of these guides, while opposing the vibrations, which are sometimes significant, created by the hydromechanic stresses resulting from the axial flow of the cooling water flowing through the plate and flange and which is collected above said plate in the upper portion of the reactor vessel, and then is discharged through appropriate outlet nozzles. The prior art solutions only partly meet these requirements, and cannot provide assurance of reliability over time.